Mercury – Gear Case Seal Kit | Outboard Lower Unit | Marine Polymer Seal | 8M0082880

Overview

If you’ve spent any time around small outboards, you know how much peace of mind comes from a lower unit that stays sealed tight. It’s one of those simple things you don’t think about often — until a worn washer lets water sneak in or gear lube drip out. The Mercury 8M0082880 Gear Case Seal Kit is the kind of quiet, dependable part that keeps your motor protected trip after trip. Whether you’re running a lightweight 5 horsepower on a tender or a hardworking 20 horsepower on a fishing skiff, this little seal helps ensure your lower unit stays healthy, dry, and ready every time you launch.

Key Features

• Gear case sealing kit designed to protect the lower unit from water intrusion
• Marine-grade polymer washer engineered for long-term sealing strength
• Blue-colored washer for easy identification during service
• Ideal for routine gear lube changes or replacing worn or damaged seals
• Precision fit designed specifically for Mercury outboard gear housings
• Helps maintain proper gear lube pressure and internal lubrication

Engine & Boat Compatibility

• Fits select Mercury propane-fueled 5 horsepower outboards (serial number 0R936270 and above)
• Fits Mercury 8 and 9.9 horsepower FourStroke models (serial number 0R008146 and above)
• Compatible with 15–20 horsepower Mercury EFI FourStroke and Mercury SeaPro outboards (serial number 0R833820 and above)
• Commonly used on dinghies, jon boats, inflatables, small fishing boats, and portable engine setups

Performance & Practical Benefits

A good seal is one of those parts that quietly does a lot of heavy lifting. When the Mercury 8M0082880 washer is in place, your lower unit stays tight and protected, keeping water where it belongs — outside the gear case. You’ll feel the difference when you drain your gear lube and see clean oil instead of the milky mixture that comes from water intrusion. It’s the kind of protection that helps your engine’s internal gears stay smooth, steady, and well-lubricated.

Installation is simple and clean. The washer seats firmly without feeling brittle or loose, and you’ll appreciate how naturally it fits into the drain and vent screw design. When you tighten things down, it gives a satisfying, secure compression — not overly soft, not too rigid. Just right.

Over time, these seals take a beating from pressure, heat, and repeated servicing. Replacing them during regular maintenance gives you a fresh start and helps extend the life of your lower unit. It’s a small step with a big payoff, especially on engines that see heavy use or run in sandy, muddy, or saltwater environments.

Why Buy OEM

There are plenty of generic washers out there, but this is one of those parts where exact fit matters. A poorly made seal can compress unevenly, fail to seat properly, or break down after a season. The Mercury 8M0082880 Gear Case Seal Kit is engineered specifically for the gear housings on these smaller outboards, ensuring a tight, reliable seal every time. It’s durable, it fits the way it should, and it helps avoid the kind of water damage that leads to expensive repairs. When a component is responsible for keeping water out of your gear case, OEM is absolutely the smart choice.

FAQ

Q1: Which engines does the 8M0082880 Gear Case Seal Kit fit?

It fits Mercury 5, 8, 9.9, 15, and 20 horsepower models listed by compatible serial ranges, including SeaPro and propane-fueled versions.

Q2: What makes this seal better than aftermarket options?

OEM seals compress evenly, fit precisely, and use marine-grade materials that hold up longer under pressure and heat.

Q3: How do I know if this is the right replacement?

Check your engine’s horsepower, serial number, and owner’s manual. If you service your own gear lube, this is likely the correct Mercury Marine part.

Q4: Can it be used in both freshwater and saltwater?

Yes. It’s designed for long-term use in either environment.

Q5: Is installation straightforward?

Very. Most boaters replace it during a routine gear lube change using basic hand tools.